DESCRIPTION The ultimate goal of the proposed research is to elucidate the genetic mechanisms by which vitamin A and its derivatives modulate the phenotype of airway epithelial cells. Vitamin A is essential for airway epithelial cell differentiation and maturation. In the absence of vitamin A, epithelial cells lose their mucocilliary differentiation and become squamous. In preliminary studies, vitamin A has been shown to regulate several airway specific genes that can be used as phenotypic markers. A novel gene that is induced by vitamin A has been isolated from a airway epithelial cDNA library. This gene has homology to members of the short-chain (alcohol) dehydrogenase (SDR) family, and specifically to retinol dehydrogenases. The novel gene may therefore be important in the metabolism of vitamin A to the transcriptional regulator retinoic acid in airway epithelial and hence important to regulation of airway epithelial phenotype. The short tem goal of this research is to characterize the novel gene. The immediate hypothesis is that the novel gene encodes a retinol dehydrogenase; and that its expression is regulated at the transcriptional level by vitamin A. The first part of the hypothesis will be tested by assaying protein extracts of cultured cells that express the novel gene for the ability to oxidize retinol to retinaldehyde the assays will be analyzed by HPLC in order to identify the substrates and products of metabolism. The second part of the hypothesis will be tested by mRNA stability assays and nuclear run on transcription assays, to discriminate between transcriptional and post-transcriptional regulation of the novel gene by vitamin A.